A conventional mounting apparatus includes, for example, as shown in FIG. 5, a top plate 1, a temperature control unit 4 formed of a cooling jacket 2 and a plate heater 3 integrated with the top plate 1, and a heat insulation plate 6 integrated with the temperature control unit 4 through a heat insulation ring 5, and has a configuration that a wafer (not shown) is attractively held on a top surface of the top plate 1, and controlled to a specific temperature by the temperature control unit 4, whereby a specific process is performed on the wafer. The top plate 1, the cooling jacket 2 and the plate heater 3 are coupled together in an inner portion (except for a central portion) of the heat insulation ring 5 by a plurality of bolts 7A arranged in a concentric circular shape at specific intervals along its Circumferential direction to thereby be integrally formed as the temperature control unit 4. Further, each center of the cooling jacket 2 and the plate heater 3 is fixed together by a bolt 7B. Furthermore, the heat insulation ring 5 is coupled to the top plate 1 and the cooling jacket 2 by a bolt 7C, while it is coupled to the heat insulation plate 6 by a bolt 7D. Meanwhile, reference numeral 8 of FIG. 5 is an insulation sheet.
Moreover, the top plate 1 is made of a material having an excellent thermal conductivity such as copper or aluminum. The surface of the top plate 1 is coated with gold, nickel or the like to prevent oxidation of the top plate 1. Further, the cooling jacket 2 has therein a coolant path 2A through which a coolant flows so that the wafer can be cool down to a specific temperature by the coolant. The plate heater 3 heats the wafer to a specific temperature through the cooling jacket 2 and the top plate 1. In addition, the temperature control unit 4 and the heat insulation plate 6 are spaced apart from each other by the heat insulation ring 5, thereby being heat-insulated from each other.
Meanwhile, the mounting apparatus is configured to attract and hold the wafer on the top plate 1 and control the temperature of the wafer based on an inspection temperature from a low temperature of minus several −10° C. to a high temperature up to +150° C. For this, the mounting apparatus which is hardly thermally deformed as a whole, and has a small heat capacity and an excellent thermal conductivity is required, and at the same time, lightweight of the mounting apparatus itself is also required. Furthermore, in order to enhance the adhesivity and the thermal conductivity between the top plate 1 and the wafer, it is also required to improve the flatness of the top plate 1.
However, since the conventional mounting apparatus produces the flatness of the mounting surface by surface processing the top plate 1, and therefore, the internal stress of the top plate 1 increases while the top plate 1 is surface-processed, the flatness of only about 5 μm is obtained. Further, since the top plate 1 is made of a metal to be easily deformed, if the cooling jacket 2 has bad flatness, the flatness of the top plate 1 is deteriorated under the influence of the cooling jacket 2. Furthermore, the top plate 1 and the cooling jacket 2 are coupled together by the bolts 7A and 7C over the entire surface thereof except for the central portion, and further formed of different metals. Therefore, due to a difference between each thermal expansion rate, it is noted that the top plate 1 is thermally deformed at a temperature range, for example, from +25° C. to +150° C., and thus, the flatness is deteriorated from 5 μm to 10 μm. Meanwhile, thickening the top plate 1 can be considered in order to reduce the influence of the cooling jacket 2. However, in this case, the heat capacity increases as the top plate 1 is thickened. Therefore, a time required for raising and lowering the temperature of the wafer becomes longer and at the same time the top plate 1 itself becomes heavy. Further, since the top plate 1 is fixed to the cooling jacket 2 and the heat insulation ring 5, when assembled, it can be known that the flatness of the assembled top plate 1 is deteriorated under the influence of the cooling jacket 2 and the heat insulation ring 5.
Further, Japanese Patent Laid-open Application No. H5-036818 discloses therein a wafer chuck formed of ceramic, i.e. SiC impregnated with Si, while Japanese Patent Laid-open Application Nos. 2005-072039 and 2000-066710 disclose a vacuum chuck using the ceramic identical with that of Japanese Patent Laid-open Application No. H5-036818.